The polyethers disclosed in this invention are comprised of ethylene oxide and propylene oxide components which are endblocked with an acyloxy group. Typically, the precursors to such materials are hydroxy endblocked by virtue of the process by which they are manufactured. In many applications for these materials, the carbinol functionality at the ends of the polymer chains are required to be capped in order to reduce the reactivity of the polymers in certain reactive systems. Many of these materials are capped with ether groups, such as methyl ether; isocyanates, such as toluene monoisocyanate; acyloxy groups, such as acetoxy, and the like.
The prior art, especially in the castable polyurethane resin, and polyurethane foam art, is replete with examples of these materials that are in the form of polysiloxane-polyoxyalkylene copolymers. The methods and materials used in capping the various polysiloxane-polyoxyalkylene copolymers are known as well.
In the polyurethane foam art, there is a special problem associated with the use of polyethylene-polypropylene copolymers as the organic segment of the polysiloxane-polyoxyalkylene copolymers. The usual procedures for manufacturing such materials results in a molecule in which one end of the polyoxyalkylene is capped with an unsaturated group such as vinyloxy or allyloxy in order to be able to react with methylhydrogenpolysiloxanes to create the polysiloxane-polyoxyalkylene copolymers. This is possible through hydrosilylation using noble metal catalysts, wherein the polysiloxanes have a certain number of methylhydrogensiloxane units in their molecules that react with the unsaturated groups of the polyoxyalkylenes to form Si--C bonds. Generally, the polyoxyalkylene copolymers can be capped before the hydrosilylation, or they can be capped after the hydrosilylation. Whatever the case, the normal preparative method for the unsaturated polyoxyalkylene copolymers is to coreact, for example, allyl alcohol with ethylene oxide and then react this polymer with propylene oxide such that the polyoxyalkylene copolymer molecule ends up with primarily secondary alcohol groups at its non-unsaturated end. In other methods, a random copolymer can be formed by reacting ethylene oxide, propylene oxide and allyl alcohol to provide a material having large numbers of carbinols on the secondary carbon atoms of the propylene glycol that is formed. Thus, one ends up with a molecule having the general formula: ##STR1## wherein the majority of the carbinols on the molecule are attached to the secondary carbon atoms. So that the polyoxyalkylene materials could be reacted into polysiloxanes, and eventually participate in, for example, polyurethane foam production as surfactants, the carbinols are quite often endblocked as was indicated supra. A common endblocker used is acyloxy. The acyloxy endblocked materials have been used for over twenty years in aqueous systems in spite of the fact that they are susceptible to hydrolytic degradation. Thus, even though the problem was not overly severe, it still remained a problem. Materials made this way and stored in environments wherein even minute amounts, e.g. 100 ppm water is also present, tended to be unstable on the shelf and hence, could not be stored with any expectation that the materials would remain stable.
It was unexpectedly found by the inventor herein that when the polyoxyalkylene random copolymer was prepared so that a significant number of the carbinols are attached to primary carbon atoms, i.e. primarily on the oxyethylene segments of the copolymer, and then endcapped with acyloxy groups, a hydrolytically stable copolymer could be made. Such a material can be made by providing a random polyoxyalkylene copolymer, and then reacting it further with additional ethylene oxide or ethylene glycol to cap the polymer with primary carbinols, i.e. "enriched" random copolymers with ethylene oxide bound carbinols.
Further, when the polyoxyalkylene copolymers of this invention were used to prepare polysiloxane-polyoxyalkylene copolymers, this benefit was imparted to such materials, even when they were stored over long periods of time and at elevated temperatures as evidenced by the accelerated data provided in the examples.